Plugs for well logging operations

ABSTRACT

A hollow body is provided with a seal by which it may be sealed within a nipple profile included in a tubing string. The body allows a wireline to be passed through it while maintaining a substantial seal. During running-in lower collet fingers engage a stop ring mounted on the body. When the plug becomes seated in the nipple profile by the weight of a logging tool also suspended on the wireline, fingers are disengaged by inward movement of external collet fingers and rollers. Consequent downward movement of the fingers allows the rope socket to push them outwardly and allows the logging tool to be lowered. An equalizing sleeve can be pulled up by the socket head from the sealing position to a raised position which allows pressure equalization above and below the plug to facilitate withdrawal thereof. Profiles on the fingers act to trap the socket head should the wireline pull out or break.

BACKGROUND OF THE INVENTION

This invention relates to logging plugs for use in oil, gas and otherwells.

To ascertain parameters of well operations such as pressure, temperatureand flow rate one or more logging tools are run down the well on loggingtool suspension means, for example an electrical logging cable or slickline. As many of these parameters in the perforation zone must bemeasured while the pressure there is different from that obtaining inthe upper part of the well down which the logging tool is run, it isnecessary for the suspension means to be passed through a logging plugwhich maintains a good, but not perfect, seal with the suspension means,and which is itself sealable within a nipple profile incorporated inproduction tubing, by-pass tubing or the well casing.

Considerations arising from typical employments of a conventionallogging plug have been discussed in our co-pending ApplicationPCT/GB89/00799 (WO 90/00667) which corresponds to U.S. Pat. No.5,099,919, which is incorporated herein by reference.

It was an aim of the earlier invention to provide a logging plug whichallowed the pressures obtaining above and below the plug to be equalizedand thus allow withdrawal of the plug and logging tools.

According to the earlier invention there was provided a logging plug forsuspension down a well, comprising a hollow body provided with sealingmeans by which it could be sealed within a nipple profile included in atubing string, the body also providing or receiving means to allowsuspension means to be passed therethrough while maintaining asubstantial seal, and an equalizing member through which the suspensionmeans could freely pass and which was arranged for sliding movementwithin said body between a first position in which communication pastsaid sealing means was prevented and a second position in whichcommunication past the sealing means was allowed.

Preferably the equalizing member had at least one port communicatingwith an axial bore through which the suspension means passed and whichin the first position was closed by a sleeve forming part of the hollowbody, and in the second position communicated with one or more portsformed through the wall of the hollow body.

Preferably again, the equalizing member was located at the lower end ofthe logging tool so that it could be displaced from the first to thesecond position by the upward impact of a logging hammer or of a loggingtool attached to the suspension means.

A disadvantage of known logging plugs, and indeed the plug according toour earlier invention, is that the plug may have to be seated inposition by the weight of a logging hammer secured to the suspensionmeans above the plug. Securing the hammer is a time-consuming operationinvolving the use of expensive pressure lock apparatus.

SUMMARY OF THE INVENTION

It is an aim of the present invention to provide a logging plug which isself-seating in a nipple profile.

According to the present invention there is provided a logging plug forsuspension down a well on logging tool suspension means, the plugcomprising a hollow body provided with sealing means by which it may besealed within a nipple profile included in a tubing string, the bodyalso providing passage means to allow said suspension means to be passedtherethrough while maintaining a substantial seal therewith, andengagement means which, in a running-in condition, are arranged to beengaged both by an element located on the suspension means and by thebody such that, in operation, the plug becomes seated in the nippleprofile by the weight of at least one logging tool also suspended on thesuspension means, the suspension means also being arranged to bedisengaged by release means operable by co-operation, in the seatedposition of the plug, with a restriction in the tubing string, to allowthe suspension means to pass downwardly through the seated plug toenable the logging tool or tools to be lowered to a desired location.

Conveniently, the logging plug according to the present invention isarranged such that upward movement of said element above the point atwhich said equalizing member reaches its second, pressure-equalizing,position causes said member to reach a pulling-out position in which ittransmits the upward force on said element to the body, enabling theplug to be withdrawn.

Preferably, the logging plug also incorporates retaining means which arecaused to assume a catching condition when the equalizing member is inthe pulling-out position, such that in the event of a suspension meansdiscontinuity, and subsequent downward movement of said element, saidretaining means are displaced to an engagement position in which saidelement is positively retained by said plug, and loss of logging toolsdown the well is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

Although the invention may be carried out in a variety of ways oneparticular embodiment thereof will now be described, by way of example,with reference to the accompanying drawings in which

FIG. 1 is a side elevation, partially in axial section, of aself-seating logging plug according to the invention, in a running-incondition; and

FIGS. 2 to 5 are each an elevation, similar to that of FIG. 1, showing amodification of the plug in, respectively, a releasing condition, anequalizing condition, a pulling-out condition and a wireline-failurecondition.

DETAILED DESCRIPTION

As seen in FIG. 1, a self-seating logging plug 10 is shown positioned ina nipple which is screwed into the bottom of a Y-tool and forms part ofa by-pass tubing string. An upper nipple profile provided by the nippleis designated by the reference 11. The plug 10 comprises a hollow body12 formed of four hollow body portions, namely a top portion 14, anupper intermediate portion 19 having annular terminal recesses 20 and21, each of the three lower portions being screwed into the bottom ofthe portion immediately above. The top body portion 14 has its upper endformed to provide a fishing neck 22.

A wireline 23 passes through all the body portions 14,16,18,19 andterminates in a rope socket 24 having a fishing neck 25 and to which oneor more logging tools (not shown) are attached. An upper collar 26 and alower collar 28 are each secured in the axial bore through the upperbody 12 and have an internal diameter such that the wireline 23 may passfreely therethrough in the presence or absence of a pressuredifferential without causing substantial friction or wear, but on theother hand allowing very little fluid flow around the wireline 23. AnO-ring 30 seals the lower collar 28 to the axial bore of the upperintermediate portion 16.

Near its lower end the lower intermediate body portion 18 is surroundedby seals 32 for sealing against a lower nipple profile 34, and by anexternal collet 36 which terminates at its upper end in a series ofcollet fingers 38, each received in a respective recess 39 provided bythe turreted lower end of the upper intermediate body portion 16. A port40 extends through the wall of the upper intermediate portion 16 at theupper end of each recess 39, and oblique aligned ports 41,42 extendthrough the external collet 36 and lower intermediate body portion 18,respectively.

Received for limited sliding movement within the two lower body portions18,19 is an internal collet 43 comprising a continuous annular medialportion 44 which provides a shoulder 45 and which is sealed to the bodyportion 18 by O-rings 46. From the medial portion 44 there extend aseries of upper internal collet fingers 48 and of lower internal colletfingers 50.

The tip of each external collet finger 38 is spaced from thecorresponding tip 69 of each upper internal collet finger 48 by a roller60 such that compression of the external collet 36 by engagement withthe nipple profile 11 above the nipple 34 disengages the upper colletfinger tips 69 from a stop ring 66 which is trapped between the bodyportions 16,18. Downward movement of the plug 10 is limited by a nippleno-go 62 which co-operates with a plug no-go 64. A stop sleeve 68 for apurpose to be described is similarly secured between the body portions18,19; and an internal profile 70, an external profile 71, and aterminal bead 72 are formed on each of the lower internal collet fingers50 for purposes which will subsequently become apparent.

Slidably housed within the internal collet 43 but normally located infixed relation thereto by a shear pin 74 is an equalizing sleeve 75which defines with the wireline 23 an annular passage 76, fluidcommunication across the sleeve 75 being provided by ports 77 and 78.The external surface of the sleeve is sealed to the internal collet 43by a lower O-ring 82 and to the body portion 16 by an O-ring 84.

To run in the above-described equalizing logging plug 10 down the tubingstring, the plug 10 in the condition shown in FIG. 1 is simply loweredwith the bottom of the equalizing sleeve 75 resting on the rope socket24. The engagement of the terminal beads 72 of the lower collet fingers50 under the fishing neck 25 prevents the plug 10 from sliding up thewireline 23 when the plug 10 encounters restrictions in the tubingstring.

When the plug 10 enters the top of the nipple profile 11 the externalcollet fingers 38 are compressed, the movement being transmitted throughthe rollers 60 to the upper collet fingers 48 to disengage the fingertips 69 from the stop ring 66. In the position (somewhat below the FIG.1 position) in which the nipple no-go 62 engages the plug no-go 64 toprevent further downward movement of the body 12, the seals 32 engagethe lower nipple profile 34. The internal collet 43 and equalizingsleeve 75 are now free to move relative to the body 12 and are carrieddown by the engagement of the fishing neck 25 with the terminal beads 72until the shoulder 45 abuts the stop sleeve 68. In this condition, whichis that shown in FIG. 2, the terminal beads 72 of the lower colletfingers 50 are free to expand into the terminal recess 21, releasing thefishing neck 25; the rope socket 24 is thus free to be lowered downhole,until the suspended logging tool is in its desired operational location.

During the production of the well a negligible quantity of well fluidwill flow between the collars 26 and 28, and the wireline 23, andthrough the annular passage 76 to be recirculated; a seal with thewireline 23 is thus established in the by-pass tubing string while stillallowing passage of the wireline 23.

When the plug 10a is in the closed condition shown in FIG. 2 there is nocommunication from the ports 40 through the body down past the seals 32to the bottom of the plug 10a: as will be seen the O-ring 84 blockscommunication to the upper end of the annular passage 76, and the O-ring82 to the lower end. The plug 10a thus effectively seals across thenipple profile 34.

If the weight of the logging tools is insufficient to move the internalcollet 43 down to the FIG. 2 position or if the lower internal colletfingers 50 release the fishing neck 25 before the internal colletshoulder 45 abuts the stop sleeve 68, the pump discharge pressure and/orhydrostatic pressure ensures that the internal collet 43 is correctlypositioned to admit the re-entrant fishing neck 25, i.e., with theterminal beads 72 in the recess 21 as shown in FIG. 2.

After pumping has ceased there may still be a considerable downwardforce on the plug 10a as explained in U.S. Pat. No. 5,099,919 usuallyrendering it operationally impossible to pull the plug 10a out of thelower nipple profile 34, and it is therefore necessary to equalize thepressure differential from above to below the plug 10a, which isaccomplished as follows.

By pulling on the wireline 23 the socket head 24 is caused to re-enterthe mouth of the body portion 19, passing the terminal beads 72 on thelower internal collet fingers 50 which are displaced into the recess 21.The continued ascent of the socket fishing neck 25 then moves theequalizing sleeve 75 upwards, together with the internal collet 43,until further upward movement thereof is prevented by engagement of thetips 69 of the upper internal collet fingers 48 with the stop ring 66,at which point the shear pin 74 is broken. The upward movement of theequalizing sleeve 75 is continued until the socket fishing neck 25 abutsthe lower shoulder the internal profile 70, as shown in FIG. 3. In thisequalizing condition the lower O-ring 82 is displaced from its seatingsurface on the internal collet 43, and communication across the plug 10ais achieved via the annular passage 76, ports 78, the annular passagebetween the equalizing sleeve 75 and internal collet 43, and the ports40.

Continued pulling on the wireline 23 causes the fishing neck 25 to bepulled past the internal profile 70 on the lower internal collet fingers50 which are free to be moved outwardly by virtue of the beads 72 andexternal profile 71 being opposite the recesses 20 and 21 respectively,the fishing neck 25 carrying with it the equalizing sleeve 75 until itsupper end abuts the collar 28 as shown in FIG. 4, thus enabling the plug10 to be returned to surface by pulling on the wireline 23.

It will be noted that in the FIG. 4 condition the upper shoulders of theinternal profiles 70 on the internal collet fingers 50 are positionedjust beneath the fishing neck 25. Should pulling on the wireline 23 beunsuccessful in unseating the logging plug 10 from the nipple 34 thewireline 23 is designed to pull out of the rope socket, as shown in FIG.5, at 90, which is a pre-determined point of weakness. Thus freed, theweight of the logging tools will carry the rope socket 24 downwardstaking with it the internal collet 43 until the external profiles 71 onthe lower fingers of the latter abut the lower shoulder of the recess 20in the lowermost body portion 19, securely trapping the fishing neck 25above the internal profiles 70, and preventing the logging tools frombeing lost downhole. It will be noted that in this condition theshoulder 45 again abuts the stop sleeve 18.

The logging plug 10a may then be retrieved, together with the loggingtools, using stronger fishing equipment.

It will be appreciated that the above-described operation of the colletfingers 38 to release the logging tool relative to the plug 10 is"selective" with regard to position in that release will only occur whenall the fingers 38 are compressed by entry into the upper nipple profile11; release of the logging tool does not occur if, for example, one ortwo fingers 38 are compressed by encountering an obstacle in the tubingstring when the plug 10 is being lowered downhole.

It will be further appreciated that the logging plug 10a shown in FIGS.2 to 5 is a slight modification of the plug 10 shown in FIG. 1. The plug10 is particularly applicable to being employed with the multi-sensorarrangements described in our co-pending Application No. PCT/GB90/00482(WO 90/12196), corresponding to U.S. Pat. No. 5,213,159 and themodification 10a differs only in the location of the seals 32 and theomission of the ports 41,42 which are necessary to permit a fluid pathinto the multi-sensor valve.

We claim:
 1. A logging plug for suspension down a well on logging toolsuspension means, the plug comprising a hollow body provided withsealing means by which it may be sealed within a nipple profile includedin a tubing string, said hollow body providing passage means to allowsaid suspension means to be passed therethrough while maintaining asubstantial seal therewith, and engagement means, which, in a running-incondition, are arranged to be engaged both by fishing means located onthe suspension means and by the body such that, in operation the plugbecomes seated in the nipple profile by the weight of at least onelogging tool also suspended on the suspension means, the suspensionmeans also being arranged to be disengaged by release meansco-operating, in the seated position of the plug, with a restriction inthe tubing string to allow the suspension means to pass downwardlythrough the seated plug to enable the logging tool or tools to belowered to a desired location.
 2. A logging plug as claimed in claim 1and additionally comprising an equalizing member through which thesuspension means may freely pass and which is arranged for slidingmovement within said body between a first position in which fluidcommunication from above said body past said sealing means to below saidbody is prevented and a second position in which such communication pastthe sealing means is allowed.
 3. A logging plug as claimed in claim 2,in which the engagement means provide an annular sealing surface towhich the equalizing member is arranged to be sealed in said firstposition.
 4. A logging plug as claimed in claim 2 arranged such thatupward movement of said fishing means above a point at which saidequalizing member reaches its second position causes said member toreach a pulling-out position in which it transmits the upward force onsaid fishing means to the body, enabling the plug to be withdrawn.
 5. Alogging plug as claimed in claim 1, in which the release means comprisea number of annularly-disposed external collet fingers arranged to bedisplaced inwardly by engagement with said restriction in the tubingstring to allow the engagement means to assume a tool lowering position.6. A logging plug as claimed in claim 5, in which the engagement meanscomprise a number of internal collet fingers corresponding to the numberof external collet fingers, each arranged, in the running-in condition,to engage a surface of the body and to be disengaged therefrom by inwarddisplacement of an external collet finger.
 7. A logging plug as claimedin claim 5, in which the engagement means comprise a number ofresilient, axially-extending fingers each provided with an internalcamming surface, which, in the running-in condition, engages saidfishing means, and also with an external abutment surface, which, in therunning-in condition, is arranged to abut the body to maintain theengagement of the camming surface with said fishing means, and in thetool lowering position is received in a recess in the body to permit thefingers to be splayed by camming action and thus allow downward movementof said fishing means.
 8. A logging plug as claimed in claim 2, andadditionally comprising retaining means which are caused to assume acatching condition when the equalizing member is in the pulling-outposition, such that, in the event of a break in the suspension means andsubsequent downward movement of said fishing means, said retaining meansare displaced to an engagement position in which said fishing means arepositively retained by said plug, and loss of logging tools down thewell is prevented.
 9. A logging plug as claimed in claim 8, in which theretaining means are constituted by an abutment face formed internally onat least one finger, and by co-operating formations on the fingers andbody arranged to maintain the abutment face in engagement with saidfishing means.
 10. A logging plug as claimed in claim 2 in which thebody includes an internal annular formation arranged to be engaged bythe engagement means in the running-in condition and act as a stopmember for the engagement means to allow relative upward movement of theequalizing member to said second position.